Using Carbon Dioxide to

Produce Better Ready Mixed Concrete

Kevin Cail, Sean Monkman and Jennifer Wagner

IntroductionCarbon dioxide emissions are recognized as a significant issue relating to cement production and the use of concrete as a building mate- rial. The industry has previously recognized a number of approaches to reduce cement emissions (IEA 20091), however, further innovative approaches are being investigated that can be a part of a portfolio strategy to achieve deeper reductions.

One potential method is to recycle captured carbon dioxide into concrete products. The method involves collecting carbon dioxide (CO2), a byproduct from industrial operations, and injecting it into fresh concrete where it becomes chemically sequestered within the concrete. After the CO2 is purified and compressed, it is trans- ported to ready mixed concrete production facilities where it is incorporated into con- crete during mixing. The result is that the CO2 is permanently embedded within the concrete, thereby becoming “sequestered” within the concrete as a mineral. The benefits of incorporating carbon dioxide into con- crete are two-fold: (1) the CO2 is chemically captured thereby reducing greenhouse gas emissions, and (2) the addition of CO2 can improve the concrete’s material properties such as compressive strength.

CarbonCureTM Technologies (CarbonCureTM) offers a technology to the concrete industry that allows for the sequestration of CO2. After successfully launching the technol- ogy in the masonry industry, the company is now applying its technology to ready mixed concrete. The CarbonCureTM Ready Mixed Concrete Technology (CarbonCureTM RMT) is now available across North America to ready mixed concrete produc- ers that are looking to appeal to the green market while improving material proper- ties such as compressive strength. The company is now working with leading concrete producers across Canada and the U.S. to install its carbon sequestration technology in their plants.

North American concrete producers now have access to a technology that repurposes waste carbon dioxide to provide concrete with more environmentally-friendly characteristics and improved mate- rial properties such as increased compressive strength.

Injecting waste carbon dioxide into concrete Working with leading concrete producers, the CarbonCure Ready Mix Concrete Technology is being installed in several concrete plants across Canada and the U.S. The technology is based on the concept of delivering carbon dioxide to ready mixed concrete during production. A tank of liquid CO2 is connected to a gas control system and manifold. The CO2 is then injected into the mixing drum whereupon it reacts with the hydrating cement to produce a calcium carbonate product similar to limestone. Since the CO2 is converted into a solid, the CO2 sequestration is permanent.

Josh Brown, director of engineering at CarbonCure Technologies, gets ready to inject carbon dioxide into concrete at a ready mixed concrete plant in March 2015.

There are two primary benefits of incorpo- rating waste carbon dioxide into concrete. In addition to the environmental impact of sequestering a greenhouse gas into concrete, the addition of CO2 can improve the con- crete’s compressive strength. The environmental benefit of sequester- ing CO2 into concrete is realized due to the fact that once CO2 is sequestered within concrete, it is removed from the air and does not contribute to the accumulation of greenhouse gases in the atmosphere. The best way to understand the potential envi- ronmental impact this technology could have is to look at the CO2 reductions that could be realized from a project using con- crete made with sequestered CO2. A project that uses 50,000 yd3 of concrete could have potentially significant reductions in the concrete’s carbon footprint. Incorporating CO2 into concrete for a project of this size would reduce CO2 emissions by 556 tonnes of CO2. This CO2 reduction is equivalent to the amount of CO2 that 25,000 trees or 460 acres of forest will absorb in a year (U.S. EPA 20152).

Incorporating CO2 into concrete can also improve the material properties of concrete. Figures 1 and 2 show the average compressive strength measured for concrete during two industrial trials of the CarbonCure Ready Mixed Concrete Technology at partner pro- duction facilities. The results confirmed that an increase in the compressive strength could be realized upon applying carbon dioxide to the concrete mix. As shown in Figure 1, the addition of CO2 resulted in a strength benefit exceeding 14 percent at all ages, including a 26 percent benefit at three days and 18 per- cent at 56 days. Figure 2 shows the results from another trial, where the optimal dose of CO2 (the bar labeled “CO2 1404”) resulted in strengths 19 percent higher at one day, 16 percent higher at 28 days and 26 percent higher at 59 days.

Figure 2: Compressive strength of concrete made without (blue bars) and with (orange bars) carbon dioxide at varying doses of CO2. Increases in compressive strength of the carbonated samples are shown as a percentage relative to the control sample.

A green opportunity for producers

Architects, engineers, contractors and developers are now looking for innovative approaches to reducing the carbon footprint of concrete to meet certification require- ments such as LEED and to provide their clients with sustainable design solutions. It is increasingly common for concrete producers to be asked to provide Environmental Product Declarations (EPDs) and Health Product Declarations (HPDs), which provide points under the U.S. Green Building Council’s new LEED version 4 program. NRMCA has made it a priority to make tools available to ready mixed concrete producers wishing to capitalize on the growing demand for EPDs and HPDs with the introduction of a robust set of programs such as the NRMCA Environmental Product Declaration Program. CarbonCure Technologies has provided dozens of EPDs and HPDs to its masonry producer partners, and can now provide EPDs and HPDs for concrete mixes produced using the CarbonCure Ready Mixed Concrete Technology.

The CarbonCure Ready Mixed Concrete Technology presents an opportunity for concrete producers looking to access the growing green building market. Moreover, the addition of CO2 to concrete can also provide material performance enhance- ments, such as increased strength, which has clear advantages for any ready mixed concrete producer looking to stay ahead of the curve.

If you are interested in learning more about how the CarbonCure Ready Mixed Concrete Technology could help your operations, please contact Kevin Cail, chief technology officer of CarbonCure Technologies, at kcail@carboncure.com or visit carboncure.com.